Stevenson and Lewis: Skate bycatch in the commercial groundfish fisheries of Alaska 
215 
Figure 3 
Annual mean exvessel price paid by processors in Alaska for big skate 
( Raja binoculata), longnose skate ( Raja rhina), and miscellaneous skates 
from 1998 through 2007. 
catch in pelagic trawls is the result of the net contact- 
ing, or at least coming very close to, the seafloor. 
Historically, skates have not been considered valuable 
by Alaska’s commercial fishermen. Even though skates 
are large fishes that represent a significant potential 
source of protein, retention of skates in the commercial 
fisheries of Alaska has been low. However, groundfish 
observer data, coupled with exvessel pricing informa- 
tion, may indicate that this situation is beginning to 
change. Overall mean retention was less than 15% in 
the late 1990s, and presumably before that time as well; 
however, it has increased to 30-35% in recent years. 
Species-level catch data collected since 2004 indicate 
that the large species (such as both species of Raja, 
Bathyraja parmifera , and B. aleutica) are retained at 
a higher rate than smaller species, and that retention 
rates for the large species are not necessarily consistent 
from year to year. The general increase in retention 
rates may reflect changes in the market value for skate 
products. Although the mean exvessel price for general 
skate catch has remained fairly stable over the past 
decade (Fig. 3), the price paid to Alaskan fishermen 
for big skates and longnose skates has risen sharply. 
Since 2004, when processors began reporting landings 
data by species owing to changes in the Fishery Man- 
agement Plan for groundfish of the Gulf of Alaska, the 
mean annual price paid for big and longnose skates has 
nearly tripled. 
Although the data presented here signify a dramatic 
improvement in the information available to fishery 
managers, some noteworthy gaps persist. The data pre- 
sented here represent only sampled hauls on vessels 
requiring observer coverage in federally managed fish- 
eries, and therefore other sources of skate bycatch are 
not represented. Commercial fishing activity in the Ber- 
ing Sea and Aleutian Islands is conducted primarily on 
large vessels, which are required to have 100% observer 
coverage, and therefore observer data should provide a 
good representation of skate bycatch in those regions. 
In contrast, many of the commercial vessels operating 
in the Gulf of Alaska are small enough that observer 
coverage is only required on 30% of fishing days or is 
not required at all. Therefore, observer data for this 
region may provide much less reliable estimates of skate 
bycatch. Because the two species of the genus Raja are 
common in the Gulf of Alaska, and are among the larg- 
est skate species in the region, the unobserved catch of 
those species is of particular concern. Disproportionate 
retention of larger skates is prevalent in many fisheries 
worldwide, and as larger, more vulnerable species are 
removed, smaller species may become more abundant 
(Russ, 1991; Agnew et al., 2000; Cedrola et al., 2005; 
Swain et al., 2005). In the North Atlantic, severe reduc- 
tion in biomass for some larger, less resilient skate spe- 
cies has been accompanied by an increased biomass for 
smaller, more resilient species (Casey and Myers, 1998; 
Walker and Hislop, 1998; Dulvy et al., 2000). Species- 
specific observer data on skate bycatch can document 
this phenomenon, but only if the data are representa- 
tive of total fishing effort. Therefore, undocumented 
sources of skate bycatch, as well as nonspecific data 
from observed longline fisheries (see above comments on 
longline species composition data), present significant 
remaining challenges to fishery managers. 
Observer data on skate bycatch in the groundfish fish- 
eries of Alaska represent a rich source of information 
for managers charged with protecting skate populations 
from future overexploitation. The species-level catch 
data now being collected by observers have facilitated 
the development of an age-structured stock assessment 
model for B. parmifera (B. Matta, personal commun. 2 ), 
which is a critical aid in setting appropriate catch lim- 
its for the species, and similar models for other species 
2 Matta, Beth. 2009. NMFS Alaska Fisheries Science Center, 
Seattle, WA 98115. 
